I read a review about a week ago comparing four liquids, and distilled water + water wetter. The distilled water had the best temps overall. Second came Feser One, which was actually non conductive (not like most others which say it, but aren't). The reviewer even splashed it on his motherboard and videocard while it was running just to see, and he wiped it off with no negative effects. FluidXP was actually rated the worst out of them all, and because it was a bit thicker than the rest, it also made the pump run a bit louder. So if you want fancy colours and 100% non-conductiveness (not really a word :() Feser One is the best choice. But if all you want is the lowest possible temperatures, go with distilled water and water wetter.
I'll see if I can find the review again.